1. Field of the Invention
The present invention relates to a radiographic examination apparatus to fluoroscope or to shoot continuously by using radiation and a method for the same.
2. Description of the Related Art
According to a conventional radiographic examination apparatus used for diagnosis or medical treatment, an X-ray image is detected along with an incident X-ray in an image intensifier (II) or a flat panel detector (FPD) after the x-ray irradiated from an X-ray tube passes through a subject. According to a radiographic examination apparatus to be used for an X-ray fluoroscopy, for example, the fluoroscopic image is obtained by a pulse output of approximately 7.5-60 fps (Frame per Second). Such radiographic examination apparatus comprises so-to-speak an automatic brightness adjustment mechanism to maintain consistent brightness by adjusting an amount of an incident X-ray by changing radiation conditions regardless subject's body size (deepness) or a part of subject's body. In addition, a radiographic examination apparatus to conduct continuous shooing approximately several frames to several 10 frames per second comprises a function to change an X-ray condition as to an X-ray pulse-output in accordance with subject's body size or a part of subject's body.
Such conventional X-ray conditions to be changed are three kinds of parameter, a tube voltage (kV), a tube electric current (mA) and a pulse width of fluoroscopy or shooting. Specifically, as radiation conditions should be changed in a broad range, for example, from an extremely low radiation dose condition on a fluoroscopy or continuous shooting through a hand (thin) to an extremely high radiation dose on examining the heart of a patient having thick (deep) chest from a diagonal direction, two parameters of tube voltage (kV) and tube electric current (mA) or three parameters including additionally a pulse width of fluoroscopy or shooting are controlled.
Then, the above parameter control is used also in order to automatically subject X-ray conditions to examination conditions, when not only an appropriate adjustment of such as brightness of image but also a continuous examination of subject's different parts by changing a relative position between an X-ray detector and a subject while fluoroscopy or continuous shooting is conducted.
Further, a control method for filament electric current, i.e. so-to-speak pre-flash, is suggested, by which the filament electric current is raised temporarily to promptly heat the filament of X-ray tube at the beginning of shooting. (Patent Document 1; JP Pub. 2006-120548).